In construction machinery, such as excavator loaders, there are used in the practice power shift transmissions or group transmissions which as a rule are designed so as to have together with switching elements for selection of the driving direction, additional switching elements with which other reduction ratios, that is, different ranges of velocity or gears for a driving direction, can be adjusted. In order to make possible mounting of such a transmission as flexibly as possible in a construction machine or in a vehicle, in the practice the switching elements have been designed of remote control, that is with crank connections instead of a linkage.
For this purpose, the transmission controls for power shift transmissions known from the practice have electrohydraulic signal converters in which are used hydraulic mechanical components that have to be electrically controlled by a selector switch.
These known electrohydraulic signal converters have the advantage of being of reasonable cost, since as a rule an additional sensor system for their main operation can be omitted. Therefore, such control device is especially adequate for low-priced systems.
However, a considerable disadvantage of these transmission controls with electrohydraulic signal converters already known is that with the control devices, when a corresponding switching device such as a shift valve is activated, a coordinated switching element will always be actuated independently of whether the shift valve has been actuated by a driver or unintentionally due to an operation error, for example, a short circuit.
In the latter case, it can happen that gearshift elements already actuated are additionally engaged. Together with possible damage to the transmission, this can lead, depending on the driving state and road surface state, to instabilities in the behavior of the vehicle and to danger of an accident.
From the practice are also known transmission controls in which said disadvantages of the above described known controls, with electrohydraulic signal converters, are avoided by additionally disposing in said transmission controls a comprehensive sensor system with signal evaluation, by means of an electronic control equipment with integrated software.
However, those electronic systems as a rule required great expenditure and incur considerable costs.